Polyamory does work for some people...the base, to me, is a strong primary relationship. Also, I believe it is possible to love two people at the same time.
The key, for you, is to decide what you want. Logically, after 9 years with the same man, the attention of another is very flattering and validating. The fact that you can discuss this with your SO is also significant to the strength of your relationship with him.
No on can decide your path, but you. I would caution, that while you are deciding your path, you step lightly, and consider those closet to you. It is easy for a man to say he would be okay with bringing another in, but, the reality can be much more difficult to accept. Also, if you both are considering opening your relationship to his friend, boundaries, and guidelines must be set before this happens, everyone must enter into it with clear expectations and "rules" to avoid confusion. If you let one in, does your SO get to let another, female, in later? Do you define it as just a triad? How involved does the third become with your children, families, finances.
And this not to assume that this will be your decision. Because, again, it your and your SO's decision to make about the path of your relationship. Just, don't get so caught up in the sudden attraction and pheromones that you stumble blindly into something that may ruin your existing strong relationship.
Anyhoo, a couple of good resources -
http://www.unmarried.org/polyamory.html
loving more is an excellent web site
If you want the crush to pass, then distancing yourself from the other guy would help. No more walks in the woods or comfy chats, never be alone with him, don't make eye contact when he gives you that "special" look. Mostly, it is mind over matter - heck, do the standard aversion therapy, rubber band on the wrist thing, and pop the heck out of that rubber band every time you think of him. Or take the "in your face" approach and tell him that you are attracted to him, you do not want to act on it, and you need his help to get past the attraction. Letting your SO know, and having him help you, is also a good path.
Good Luck
God Bless